Magneto-optic current sensors have found widespread application as a substitute for conventional current transformers to provide measurement of currents in high voltage systems. The magnetic field produced by the current flow effects a rotation of a light beam in accordance with the Faraday effect. The rotation of the light beam is indicative of the magnitude of the current flow. In the construction of precision AC and DC magneto-optic sensors for use in applications requiring long-term stability, it is necessary to provide for automatic compensation for drift which may result from aging of the components, noisy environment, etc.